Cai Yangyang, Luo Xiaowen, He Xiaoyuan, Tang Changyuan
School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou, China.
Huizhou Water Bureau, Huizhou, China.
Ecotoxicol Environ Saf. 2021 Jan 15;208:111713. doi: 10.1016/j.ecoenv.2020.111713. Epub 2020 Dec 8.
A novel Microcystis bloom caused by Microcystis densa has occurred in a typical subtropical reservoir every spring and summer since 2012, and it has caused several ecological and economic losses. To determine the environmental factors that influence the growth and physiological characteristics of M. densa, we investigated the variations in physicochemical factors and M. densa cell density from 2007 to 2017. The results showed that the urea-N concentration increased significantly (from 0.02 ± 0.00-0.20 ± 0.01 mg N l), whereas other factors did not vary significantly. NO-N and urea-N concentrations were higher than the NH-N concentration during the M. densa bloom. The nitrogen composition changed, and urea-N and NO-N became a major nitrogen sources in the reservoir. Water temperature and increased urea-N concentrations were the primary factors that influenced variations in M. densa cell density (45.5%, p < 0.05). Laboratory experiments demonstrated that M. densa cultured with urea-N exhibited a higher maximum cell density (9.8 ± 0.5 × 10 cells l), more cellular pigments for photosynthesis (chlorophyll a and phycocyanin) and photoprotection (carotenoid), and more proteins than those cultured with NH-N and NO-N. These results suggested that M. densa cultured with urea-N exhibited preferable growth and physiological conditions. Moreover, M. densa exhibited an increased maximum specific uptake rate (0.93 pg N cell h) and reduced half-saturation constant (0.03 mg N l) for urea-N compared with NH-N and NO-N, suggesting that M. densa preferred urea-N as its major nitrogen source. These results collectively indicated that the increasing urea-N concentration was beneficial for the growth and physiological conditions of M. densa. This study provided ten years of field data and detailed physiological information supporting the critical effect of urea-N on the growth of a novel bloom species M. densa. These findings helped to reveal the mechanism of M. densa bloom formation from the perspective of dissolved organic nitrogen.
自2012年以来，每年春夏季节，一种由密集微囊藻引发的新型微囊藻水华都会在一个典型的亚热带水库出现，并造成了若干生态和经济损失。为了确定影响密集微囊藻生长和生理特征的环境因素，我们调查了2007年至2017年期间物理化学因素和密集微囊藻细胞密度的变化情况。结果显示，尿素氮浓度显著增加（从0.02±0.00增至0.20±0.01毫克氮/升），而其他因素变化不显著。在密集微囊藻水华期间，硝态氮和尿素氮浓度高于铵态氮浓度。氮的组成发生了变化，尿素氮和硝态氮成为水库中的主要氮源。水温升高和尿素氮浓度增加是影响密集微囊藻细胞密度变化的主要因素（45.5%，p<0.05）。实验室实验表明，与用铵态氮和硝态氮培养的密集微囊藻相比，用尿素氮培养的密集微囊藻具有更高的最大细胞密度（9.8±0.5×10个细胞/升）、更多用于光合作用的细胞色素（叶绿素a和藻蓝蛋白）和光保护色素（类胡萝卜素）以及更多蛋白质。这些结果表明，用尿素氮培养的密集微囊藻具有更好的生长和生理条件。此外，与铵态氮和硝态氮相比，密集微囊藻对尿素氮的最大比吸收率增加（0.93皮克氮/细胞·小时），半饱和常数降低（0.03毫克氮/升），这表明密集微囊藻优先选择尿素氮作为其主要氮源。这些结果共同表明，尿素氮浓度的增加有利于密集微囊藻的生长和生理条件。本研究提供了十年的现场数据和详细的生理信息，支持了尿素氮对新型水华物种密集微囊藻生长的关键作用。这些发现有助于从溶解有机氮的角度揭示密集微囊藻水华形成的机制。
